Several reports have described an inverse relationship between the frequency of infections and various malignancies. In this paper results of a hospital-based case control study on 139 melanoma patients and 271 suitable selected controls are presented, addressing the question of whether this relationship exists with respect to malignant melanoma while simultaneously controlling for the effects of other risk factors. Data on childhood diseases (group I), febrile diseases of adulthood (group II) and common febrile infections within a 5-year period prior to the diagnosis of melanoma (group III) were collected using a standardized interview. Group I diseases did not show a marked influence on the risk of malignant melanoma. Considering group II diseases, a significant protective effect was determined for chronic infectious diseases (OR = 0.32) and also for wound infections, abscesses and furunculosis (OR = 0.21). In group III, herpes simplex infections (OR = 0.45) and influenza/common cold (OR = 0.32) substantially reduced the melanoma risk. This effect was less pronounced for gastroenteritis (OR = 0.52). Analysis of the cumulative influence of infections pointed to a strong dose-response relationship between the frequency of febrile infections in adulthood and malignant melanoma. In particular, the risk reduction was striking when two or more febrile infections were compared to no febrile infections in group II (OR = 0.09) and group III (OR = 0.20). The study confirms the hypothesis that an inverse relationship exists between febrile infections and malignant melanoma, but these results have to be interpreted cautiously due to the inherent limitations of the case-control design.(ABSTRACT TRUNCATED AT 250 WORDS)